Embodiments in accordance with the present invention relate to a radio frequency identification (RFID) device, and more particularly, to a cell array technology of a resistive random access memory (ReRAM) device using a resistive switch device (RSD).
In general, a ReRAM is a nonvolatile memory device which stores data by changing an electrical resistance of a material by applying an external voltage to a thin film.
FIGS. 1 and 2 are diagrams showing the cross-sectional structure and operation principle of an RSD in a conventional ReRAM.
The RSD has a structure in which a resistive switch 11 is disposed between a top electrode 10 and a bottom electrode 12. The top electrode 10 and the bottom electrode 12 are formed of a metal such as platinum Pt, and the resistive switch 11 is formed of a resistive insulation layer such as TiOx.
Research into the ReRAM having the above-described configuration has been conducted since the 1960's. In general, the ReRAM (memristor) has a metal insulator metal (MIM) structure using a transition metal oxide. Accordingly, when an appropriate electric signal is applied to the ReRAM, the memory characteristic of the ReRAM changes from a high-resistance non-conductive state (off state) to a low-resistance conductive state (on state).
The ReRAM may be classified into a current-controlled negative differential resistance (CNDR) device and a voltage-controlled negative differential resistance (VNDR) device, depending on the electrical method for embodying on/off characteristics.
Materials exhibiting ReRAM (memristor) characteristics may be categorized as follows.
A first category comprises materials such as colossal magneto-resistance (CMR) and Pr1-xCaMnO3 (PCMO). These materials may be inserted between electrodes and a resistance change caused by an electric field can be used to store data.
A second category comprises binary oxides such as Nb2O5, TiO2, NiO and Al2O3. These materials can be prepared to have a non-stoichiometric composition and used as a resistance controlled material.
A third category comprises chalcogenide materials. These materials change states (i.e., crystalline or amorphous) by flowing a high current like in the case of a phase change random access memory (PRAM), and a resistance difference caused by a change in a threshold voltage of an ovonic switch can be used.
A fourth category comprises chromium (Cr) or niobium (Nb) doped into materials such as SrTiO3 and SrZrO3. The doping can change the resistance state of these materials.
Finally, silver (Ag) (or the like having a high ion mobility) may be doped into a solid electrolyte such as GeSe. This material can then be manufactured into a programmable metallization cell (PMC) having two resistance states. The state depends on whether a conductive channel is formed within a medium by an electrochemical reaction.
In addition, materials having memory characteristics through the implementation of two stable resistance states or process methods thereof have been reported.